1. Field of the Invention
The invention relates to processes for producing urea/formaldehyde type resins.
2. Description of the Prior Art
Structures and powders similar to those made by the process of this invention have been made by acid catalysis of amine/aldehyde solutions in the following manner:
At room temperature (unless otherwise desired), a water solution containing the urea-formaldehyde (UF) prepolymer (and any other co-resins to be used) is added to a second water solution containing the acid catalyst and any additives (polymeric plasticizers, etc.) which are employed. This mixtue is agitated by hand just enough to provide thorough mixing, but no more than that. If desired, the mixture may be poured immediately into a mold other than the container in which it was mixed. Once gelation or polymerization has begun, however, the OPUF reaction mixture should be allowed to remain undisturbed. Gelation will generally begin within about one to five minutes after mixing, and in most cases is evidenced by a change from a clear solution to a white, opaque one, followed by rapid hardening of the solution. In general, the OPUF structures which were formed at room temperatures were allowed to remain undisturbed overnight (in a hood to facilitate solvent evaporation), then dried in a vacuum oven at or slightly be lightly below 50.degree. C. Other similar drying method may also be used.
A somewhat different method of preparation was used for all OPUF materials containing a melamine/-formaldehyde resin, as these cure above room temperature. In the case, the resin and catalyst solutions were each warmed to about 40.degree. C. before mixing them together, and then immediately after mixing the "OPUF" mixture was placed in an oven at .about.55.degree.-60.degree. C. to promote curing. Drying was simply continued under the same conditions, as it was found that vacuum drying resulted in severe sample shrinkage, probably due to incomplete cure before the vacuum was applied.
The size and shape mold or container employed in casting was determined by the desired end use for the OPUF sample. In general, it was preferable to use polyethylene or polypropylene containers, as their relative porosity assisted in the drying, and there was little or no adhesion to the surface. Special Teflon molds were prepared for casting of cigarette filter rods.
The acid catalyst used for virtually all of this work was concentrated phosphoric acid. Other organic or inorganic acids may be employed in its place, however. Different concentration levels of the phosphoric acid catalyst were employed depending on which of the various resins were used in OPUF formation.
A novelty search of the process of this invention resulted in three patents being reported and these were as follows:
U.S. Pat. No. 2,345,543 describes electrophoresis of colloidal resin solutions of resins such as melamineformaldehyde resin made by acid polymerization but not cured. These colloidal solutions are made by the acid condensation process well known in the art and constitute relatively high molecular weight resin as compared with the low molecular weight prepolymer solutions used in the process of the present invention. Electrophoresis by definition is the migration of suspended particles in an electric field.
U.S. Pat. No. 2,612,483 relates to a delayed-acting hardener for formaldehyde-urea adhesives and coating compositions, and also to the preparation of formaldehyde-urea adhesives and coating compositions having delayed-hardening properties. A prepolymer aqueous solution or dried product is all that is involved here with no electrolysis; furthermore, the prepolymer is made by a different process and has a different composition.
U.S. Pat. No. 3,449,228 describes ungelled reaction products of an amine-aldehyde condensation product and a phenol or polyol in the presence of an acid to provide vehicles for water dispersed compositions that are applied by electrodeposition. Preferably, the reaction product is employed in combination with a poly-carboxylic acid resin. The reaction products described are acid catalyzed high molecular weight resins and as stated are preferably used in combination with a polycarboxylic acid resin such as an alkyd resin. Also it should be noted that the examples, except Example 3, contain organic coupling solvents to facilitate laying down smooth continuous coatings, and in all the electrodeposition examples an alkyd resin was used together with the aminealdehyde reaction products. Under these conditions the method of the patent would do exactly what it was designed to do--provide a smooth continuous coating on the electrode.